Data processors are typically designed to meet specific product needs. For example, certain products such as multimedia mobile phones can at various times need either high performance or low power consumption. For example when running certain games, a multimedia mobile phone needs the microprocessor to provide high performance. However when running other tasks such as EMAIL and voice calling, the multimedia mobile phone needs much lower performance from the microprocessor. These varying processing environments make it difficult for the microprocessor designer to achieve the right balance between performance and preservation of battery life.
Power gating is one approach used for preservation of battery life. Power gating generally uses a metal oxide semiconductor field effect transistor (MOSFET) with a higher threshold voltage (VTH) and a lower leakage current to switch power on or off to lower VTH transistors that form the functional circuits. A data processor typically has multiple functional units, for example, central processing unit (CPU) cores. Each core has sub-functional units such as a microcode unit and a data cache. When the data processor is executing instructions that will not use microcode sequences, the data processor gates off clocks and power to the microcode unit to conserve power. Since data processors and their corresponding functional units continue to increase in complexity, thus increasing overall power consumption demands, continued improvement, focus, and refinement of techniques for reducing power consumption of integrated circuits is highly desired.
In the following description, the use of the same reference numerals in different drawings indicates similar or identical items. Unless otherwise noted, the word “coupled” and its associated verb forms include both direct connection and indirect electrical connection by means known in the art, and unless otherwise noted any description of direct connection implies alternate embodiments using suitable forms of indirect electrical connection as well.